Known ground based radar interferometry measurements can be used to monitor movement of surfaces and have the potential of sub-millimeter accuracy. These measurements typically involve obtaining radar images at different times and using shifts in reflected radiation to determine movement. Some applications for these measurements include identifying slope failure in open pit mines and monitoring movement of volcanoes or glaciers.
As used herein, ground based radar interferometry measurements include a number of slightly different radar interferometry techniques. The different techniques use the same basic process of performing radar scans across a surface, detecting radiation reflected from the surface, and comparing the phase or amplitude of reflected waves between the different scans. Depending on the specific technique, the radar images may be obtained from the same or different locations. Examples of known radar interferometry techniques include synthetic aperture radar (SAR) interferometry, differential SAR interferometry (DInSAR), and slope stability radar (SSR). Many other radar interferometry techniques exist and can be used with the methods described herein.
One source of error in radar interferometry measurements is the delay of radar waves propagating through air. In a vacuum, the waves travel at the speed of light, but in the air, the waves travel at a speed less than the speed of light. The speed in air is dependent on atmospheric conditions (e.g., temperature, pressure, humidity). The speed in air is also dependent on the frequency of the waves. Changes in the atmospheric conditions between radar scans and along a transmission path can change the speed of the waves and thus introduce error into the measurements.
Improved methods are constantly desired for reducing error (and improving accuracy) of radar interferometry measurements.